Tubular-shafted surgical instrument

ABSTRACT

A tubular-handled surgical instrument has two mutually articulated grip shanks. A tube is secured on one of the shanks, with a tool fitted at its end. A rod-like actuator for the tool is fitted to move longitudinally in the tube and articulated on the other shank via a cylindrical or spherical end. A releasable connection is provided between the tube and the actuator on the one hand and between the two shanks on the other. The tube is insertable into a tubular recess in one shank and axially securable therein by at least one radially movable spherical locking member making a friction fit with the tube in one end position. The radial movement of the locking member is limited by a stop bearing on the outside of the locking member formed by a sleeve axially movable on the tubular recess. The sleeve is movable in relation to the locking member in such a way that the locking member can be moved radially outwards to differing extents.

BACKGROUND OF THE INVENTION

The invention relates to a tubular-shafted surgical instrumentcomprising two handle parts articulatedly connected to each other, atube held on one handle part, a tool mounted at the end of the tube, arod-shaped actuating element for the tool, the actuating element beingmounted for longitudinal displacement in the tube and beingarticulatedly connected to the other handle part via a cylindrical orspherical end, and a releasable connection between tube and actuatingelement, on the one hand, and the two handle parts, on the other hand,the tube being pushable into a tubular receptacle on the one handle partand axially fixable therein by at least one radially moveable lockingbody which in an end position enters into a positive connection with thetube, and a retaining member being mounted on the other handle part, theretaining member partly embracing the cylindrical or spherical end ofthe actuating element in one end position and being moveable intoanother end position in which the cylindrical or spherical end isremovable from the other handle part in the longitudinal direction.

In tubular-shafted instruments of this kind (GB 2 140 735 A), which canbe employed in a wide variety of ways, it is important to be able todisassemble the instrument as completely as possible for the purposes oftool exchange and cleaning.

Instruments of this kind, wherein the handle parts can be connected tothe tube and to the actuating element via threaded connections, areknown. The making and releasing of the connection take a relatively longtime as fine threads, which require a large number of turnings, normallyhave to be used. It is also difficult to connect the concentric partssimultaneously in this way, as two different connections have to bemade.

Surgical instruments of the kind described at the outset are already onoffer (AESCULAP Main Catalog, 1991 edition, page 647). It is, however,necessary to provide a separate radially protruding part for the fixing,which, under certain circumstances, can complicate the making andreleasing of the connection.

The object of the invention is to so design a generic instrument thatthe making and releasing of the connection between tube and actuatingelement, on the one hand, and the handle parts, on the other hand, isfacilitated, and, in addition, locking and unlocking of the releasablemounting of the tool are also to be facilitated.

SUMMARY OF THE INVENTION

This object is accomplished in accordance with the invention in asurgical instrument of the kind described at the outset by the lockingbody being a ball, by the radial movement of the locking body beingdelimited by a stop resting against the outer side of the locking body,the stop being formed by a sleeve axially displaceable on the tubularreceptacle, by the sleeve being displaceable relative to the lockingbody such that the locking body is radially outwardly displaceable todifferent extents, [locking body . . . radially . . . to differentextents], by the sleeve forming a stop for an outer tube which ismounted for axial displacement on the tube and in the pushed forward endposition locks the releasable mounting of the tool at the opposite endof the tube, and by the sleeve being displaceable in the directiontowards the handle parts in order to release the locking of the tube.

Accordingly, separate, displaceable closure elements which can each bedisplaced or turned by a movement between a closed position and an openposition are used for both the tube and the actuating element, and sothe releasing and connecting are very easily effected. In particular,these operations can be carried out very quickly.

The design of the locking of the tube in the one handle part as balllocking mechanism facilitates the making and also the releasing of thisconnection quite considerably. Ball locking mechanisms are known per seas quick coupling for surgical instruments (WO 91/05514), but theseknown quick couplings are mainly employed for connecting surgicalinstruments to holders or extensions. It is not known from theaforementioned publication to use a ball locking mechanism forconnecting the shaft of a tubular-shafted instrument to a handle part.

To release the tube from the receptacle it is sufficient to displace thesleeve on the tubular receptacle into an end position, and the lockingbody can then release the tube in the radial direction. The sleevedisplaceable on the tubular receptacle not only fixes the locking bodywhich fixes the tube in the tubular receptacle, but also an outer tubeon the tube, and the outer tube, in turn, forms at the front end of thetube a lock for an exchangeable tool.

It is advantageous for the sleeve to be moved in a spring-loaded mannerinto the end position in which the path of displacement of the lockingbody is limited to the greatest extent. The spring thus always displacesthe sleeve into the locking position. Only against the force of thisspring is release of the axial fixing of the tube in the receptaclepossible.

In another embodiment, provision may be made for the tubular receptacleto form a stop for an outer tube which is mounted for axial displacementon the tube and in the pushed forward end position locks the releasablemounting of the tool at the opposite end of the tube. In thisembodiment, the outer tube can only be displaced on the tube when thetube is pulled out of the tubular receptacle, i.e., in order to exchangethe tool, the entire instrument must first be separated.

It is expedient for the tube to be secured against rotation about thelongitudinal axis of the tube by engagement of projections and recesseswhen it is pushed into the tubular receptacle. A defined position of thetool plane is thus attainable. Provision may be made for projections andrecesses to [engage in different angular positions], and by brieflyseparating the tube from the instrument, the operator can thusselectively turn the tube to different angular positions and fix it inthese.

In a modified embodiment, provision may also be made for the tubularreceptacle to be mounted for rotation about its longitudinal axis on thehandle part. By turning this tubular receptacle, the tube with the toolmounted thereon can be turned to the desired position and so theoperator is completely free in the angular positioning of the tool.

In a first preferred embodiment, provision may be made for the retainingmember to be constructed as a collet chuck which in the released stateallows entry or exit of the spherical or cylindrical end by bending openelastically and in the closed state embraces the spherical orcylindrical end unreleasably. Such a collet chuck can be locked by, forexample, axial pushing into a sleeve. If desired, this pushing-in can beeffected by a threaded nut.

In another embodiment, provision is made for the retaining member to bemounted for swivel movement on the other handle part and to engage inthe closed state in a section of the actuating element adjacent to thespherical or cylindrical end, the outer dimensions of the sectiontransversely to the longitudinal direction of the actuating elementbeing smaller than those of the spherical or cylindrical end. To releasethe rotary connection between actuating element, on the one hand, andhandle part, on the other hand, it is, therefore, sufficient to swivelthe retaining member on the handle part, i.e., one manual maneuversuffices to selectively attain the closed state or the released state.

It is particularly advantageous for the retaining member to have areceiving space for the spherical or cylindrical end with an openingwhich has a larger region sufficient for passage of the spherical orcylindrical end therethrough, and a smaller region which is too narrowfor passage therethrough, and for the two regions to be selectivelymoveable in the longitudinal direction of the actuating element in frontof its spherical or cylindrical end by movement of the retaining member.The receiving space encloses the spherical or cylindrical end andthereby reliably transmits both pulling and pushing movements. Solely byswivelling the retaining member, it is possible to release the actuatingelement, namely when the larger region of the opening is oriented in thelongitudinal direction of the actuating element.

It is expedient for the actuating member to be positionable in its endpositions by elastic detent members.

In particular, the opening of the receiving space can be ofkeyhole-shaped design.

DESCRIPTION OF THE DRAWINGS

The following description of preferred embodiments serves in conjunctionwith the drawings to explain the invention in further detail. Thedrawings show:

FIG. 1 a side view of a tubular-shafted instrument which can bedisassembled;

FIG. 2 a longitudinal sectional view of the front part and the centralpart of the tubular-shafted instrument of FIG. 1;

FIG. 3 an enlarged longitudinal sectional view of the central part ofthe tubular-shafted instrument of FIG. 1 in the unlocked state;

FIG. 4 a longitudinal sectional view of the tubular-shafted instrumentof FIG. 1 in the region of the releasable mounting of the actuatingelement on the handle part with the retaining member locked;

FIG. 5 a view similar to FIG. 4 with the retaining member open;

FIG. 6 a view similar to FIG. 4 of a modified embodiment of a retainingmember in the closed state;

FIG. 7 a view of the retaining member in the direction of arrow A inFIG. 6;

FIG. 8 a view similar to FIG. 4 of a retaining member in the form of acollet chuck in the closed state;

FIG. 9 a view similar to FIG. 8 with the collet chuck in the open state;

FIG. 10 a view similar to FIG. 4 of a modified embodiment of a pivotableretaining member; and

FIG. 11 a sectional view along line 11--11 in FIG. 10.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The tubular-shafted instrument illustrated in the drawings comprises twohandle parts 1 and 2 which are pivotably connected to each other andeach have a finger opening 3 and 4, respectively. The two handle parts 1and 2 are pivotably connected to each other by a screw connection 5.Held on a handle part 1 is a shaft 6 having located at the free endthereof a tool 7 which can be in the form of, for example, scissors orforceps. Arranged for longitudinal displacement in the interior of theshaft 6 is a rod-shaped actuating element 8 which is articulatedlyconnected, on the one hand, to the tool 7, and, on the other hand, tothe other handle part 2 so that during opening and closing of the handleparts 1 and 2, the tool 7 can be opened and closed by a pulling orpushing movement of the actuating element 8.

In the illustrated embodiment, this tool 7 comprises two parts 10, 11,which are rotatably mounted on a holder 9 and are pivotably connected tothe actuating element 8 via gear means 12 (FIG. 2). This holder 9 isreleasably connected to a tube 13. For this purpose, the holder 9carries an extension 14 which reaches into the tube 13 and has acircumferential groove 15. At its free end, the tube 13 is divided up bylongitudinal slots into tongues 16 which can bend open elastically andat their free end are bent inwardly. These tongues 16 surround theextension 14 and reach with their bent end into the circumferentialgroove 15 so that the extension 14 is fixed in the axial direction inthe tube 6. The tongues 16 are held permanently in this position by anouter tube 17 which is longitudinally displaceable on the tube 13 beingpushed over the tongues 16 so that the tongues 16 are prevented frommoving radially outwardly. The outer tube 17 thus forms a lock which canonly be released when the outer tube 17 is pushed back over the tongues16.

The tube 13 and the outer tube 17 displaceably mounted thereon togetherform the shaft 6 which can be releasably connected to the handle part 1.To this end, this handle part 1 carries a tubular receptacle 18 which,if desired, may be rotatable relative to the handle part 1 about thelongitudinal axis of the receptacle 18. Insertable into this receptacle18 is the tube 13, the outer diameter of which corresponds to the innerdiameter of the receptacle 18. At its end pushed into the receptacle 18,the tube 13 has longitudinal slots 19 into which a projection 20 held inthe tubular receptacle 18 protrudes.

The tube 13 is thereby non-rotatably mounted in the receptacle 18.Several longitudinal slots may be provided so that the tube 13 can befixed in different angular positions in the receptacle 18.

Mounted in a radial bore 21 of the tubular receptacle 18 in the form ofa ball is a locking member 22 which extends into a recess 23 in theouter jacket of the tube 13 when the tube 13 is pushed into thereceptacle 18. In a way which is not apparent from the drawings, theradial bore 21 is of not quite continuous construction on the inner sideso that even when the tube 13 is missing, the ball 22 cannot fallradially inwardly out of the radial bore 21. Outwardly, however, theradial bore 21 is of continuous construction so the ball 22 is freelymoveable radially outwardly.

A sleeve 24 surrounding the receptacle 18 is mounted for displacement inthe longitudinal direction on the tubular receptacle 18. In an annularspace 25 located between the sleeve 24 and the receptacle 18, the sleeve24 surrounds a helical spring 26. The latter is supported, on the onehand, on a step 27 of the sleeve 24, and, on the other hand, on a step28 of the receptacle 18 and thus acts upon the sleeve 24 with a forcewhich displaces it in the direction of the tool 7. The step 28 is guidedin a longitudinal groove 29 of the sleeve 24 so the sleeve 24 is therebysecured against rotation relative to the receptacle 18.

The movement of the sleeve 24 in the direction towards the tool 7 isdelimited by the sleeve 24 striking the outer tube 17 and thusdisplacing the latter into its foremost position in which the tongues 16are locked (FIG. 2). Therefore, only when the sleeve 24 is pushed backagainst the action of the helical spring 26 can the outer tube 17 bepushed back so far that the holder 9 can be pulled out of the tube 13.

It is also possible for the sleeve 24 to be permanently connected to theouter tube 17. Exchange of the tool 7 is then only possible when thetube 13 has been pulled out of the receptacle 18.

In an embodiment not illustrated in the drawings, provision could alsobe made for the outer tube 17 to strike the receptacle 18. In this case,too, for displacement of the outer tube 17, it would be necessary topull the tube 6 out of the receptacle 18. In this case, the movement ofthe sleeve 24 could be delimited by another suitable stop.

The sleeve 24 rests with its inner wall against the outer side of thereceptacle 18 such that the radial bore 21 is closed and so when thehelical spring 26 is relaxed, movement of the ball 22 radially outwardlyis prevented. The dimensions are such that in this case the ball 22reaches into the recess 23.

When the sleeve 24 is pushed into an open position, with the helicalspring 26 being compressed, a circumferential groove 30 on the innerside of the sleeve 24 is moved over the radial bore 21 so that the ball22 is then radially outwardly displaceable to a limited extent in theradial bore 21, more specifically, to the extent that the ball 22emerges completely from the recess 23. In this position, the axialfixing of the tube 13 in the receptacle 18 which is brought about by theball 22 is released, and, therefore, in this position, the tube 13 canbe pulled out of the receptacle 18.

The rod-shaped actuating element 8 extends through a central bore 31 ofthe extension 14 and protrudes rearwardly beyond the tube 13, morespecifically, to the extent that it also protrudes from the handlepart 1. In this region, the rod-shaped actuating element 8 carries aspherical end 32 which is connected to the actuating element 8 by aconnecting section 33 with a smaller outer diameter.

The spherical end 32 forms an articulated connection with the secondhandle part 2.

For this purpose, in a first embodiment described in FIGS. 4 and 5, aswivel lever 34 is mounted on the handle part 2 for swivel movementabout a horizontal axis extending transversely to the longitudinaldirection of the actuating element 8. The swivel lever 34 has a blindhole bore 35 which is open on one side thereof and communicates with theenvironment via a longitudinal slot 36 extending parallel to itslongitudinal direction. The diameter of the blind hole bore 35corresponds essentially to the outer diameter of the spherical end 32,the width of the longitudinal slot 36 is chosen smaller and correspondsessentially to the diameter of the actuating element 8 in the narrowerconnecting section 33. The swivel lever 34 can be swivelled between aclosed position (FIG. 4) and an open position (FIG. 5) and is fixed inboth end positions by a ball 39 which engages resiliently in recesses 37and 38, respectively. In the closed position, the spherical end 32 isreceived in the blind hole bore 35. This blind hole bore 35 thus forms areceiving space for the spherical end 32. In this position of the swivellever 34, the blind hole bore 35 is upwardly open, i.e., perpendicularto the longitudinal direction of the actuating element 8 so that it isimpossible to pull out the actuating element towards the front side ofthe instrument.

In the open position illustrated in FIG. 5, the open end of the blindhole bore 35 points in the direction of the actuating element 8 and sothe latter can be pulled out of the instrument in the direction of thearrow indicated in FIG. 5. In this embodiment, the fixing of theactuating element is brought about solely by swivelling the swivel lever34, which thus assumes the function of a retaining member for theactuating element 8.

In the embodiment of FIGS. 6 and 7, a very similar solution isillustrated, and, therefore, like parts bear the same referencenumerals. In this case, the swivel lever 34 is not fixed in the endpositions by a spring-loaded ball, but by a holding pin 40 which snapsresiliently into notches 41, 42 of the swivel lever 34. Herein, theelasticity of the material used for the swivel lever can be sufficientto allow the necessary displacements.

In the embodiment of FIGS. 8 and 9, a collet chuck 44 is mounted on thehandle part 2 for swivel movement about a horizontal axis 45 arrangedtransversely to the longitudinal axis of the actuating element 8. Thiscollet chuck 44 comprises a bearing sleeve 43 and an internally threadedsleeve 47 which is mounted so as to be rotatable but axially immoveablein the bearing sleeve 43 and has a gripping part 46. In the internallythreaded sleeve 47 a tube section 48 is screwed into an external thread49 which is pulled more or less deeply into the bearing sleeve 43 whenthe gripping part 46 is rotated. At the free end of the tube section 48,regions 51 which are elastically bendable radially outwardly are formedby longitudinal slots 50 and surround a spherical cap-shaped receivingspace 52, the dimensions of which correspond to the outer dimensions ofthe spherical end 32 of the actuating element 8. When the regions 51bend open elastically, the spherical end 32 can be pushed into thespherical cap-shaped receiving space 52 so that the regions 51 partlyembrace the spherical end 32 articulatedly.

This connection is releasable again at any time so long as the regions51 are elastically bendable outwardly, as illustrated in FIG. 9.However, by turning the gripping part 46, the internally threaded sleeve47 can be pulled so far into the bearing sleeve 43 that the elasticregions 51 rest against the inner side of the bearing sleeve 43 and arethereby prevented from elastic deformation outwardly. This isillustrated in FIG. 8. The spherical end 32 is thereby unreleasably butarticulatedly fixed in the receiving space 52. To release thisconnection it is sufficient to turn the gripping part 46 in order topush the internally threaded sleeve 47 so far out of the bearing sleeve43 again that the elastic regions 51 are outwardly bendable.

In the embodiment of FIGS. 10 and 11 there is inserted in a verticalbore 53 of the handle part 2 a swivel body 54 which is rotatable aboutthe vertical axis of the bore 53. Arranged in the swivel body 54coaxially with the bore 53 is a blind hole bore 55 which communicateswith the outer space via a transversely arranged keyhole-shaped opening56. In a first position, the narrow region of the keyhole-shaped opening56 is arranged in the longitudinal direction of the actuating element 8so that the larger spherical end 32 is prevented from exiting; in theother end position, however, the larger part of the keyhole-shapedopening 56 is arranged in this direction and so in this position thespherical end 32 can exit from the opening 56. In this embodiment, too,the swivel body 54 rotatable, in this case, about the vertical axis,could be fixed by detent members in the end positions. This is not shownexpressly in the drawings.

In each case, when assembling the described instrument, the holder 9with the tool 7 is first pushed into the front end of the tube 13 untilthe tongues 16 snap into the circumferential groove 15. The actuatingelement 8 permanently connected to the tool 7 is thereby guided throughthe bore 31, and the free end of the actuating element 8 protrudes atthe rear side of the tube 13 beyond the latter.

To fix the connection between tool 7 and tube 13, the outer tube 17 canbe displaced such that it covers the tongues 16. This unit is thenpushed into the tubular receptacle 18, and the sleeve 24 issimultaneously displaced against the action of the helical spring 26.Unimpeded entry of the tube 13 into the receptacle 18 is thereby madepossible, without the ball 22 preventing this entering movement. Whenthe tube 13 is pushed in, the projection 20 enters one of thelongitudinal slots 19 and thereby aligns the tube into the desiredangular position in the circumferential direction. Once the desiredpush-in depth is reached, the sleeve 24 is released so it moves into theclosed position under the action of the helical spring 26 and therebypushes the ball 22 into the aligned recess 23 of the tube 13. The tube13 is thereby fixed in the axial direction in the receptacle. This alsoresults in a fixing of the outer tube 17 on the tube 13, and so the tool7 is now also permanently locked in the tube 6.

During this pushing-in movement of the tube 13, the spherical end 32 ofthe actuating element 8 has entered the retaining member which is in theopen position. By moving the retaining member into the closed position,the spherical end 32 is partly articulatedly surrounded by the retainingmember, and, in addition, the end 32 is prevented from being displacedin the direction of the actuating element 8. Pulling and pushing forcescan thus be transmitted from the handle part 2 to the actuating element8.

In order to disassemble the instrument, the procedure is carried out inreverse order.

We claim:
 1. A tubular-shafted surgical instrument comprising:two handleparts articulatedly connected to each other, a tube held on one handlepart, a tool releasably mounted at an end of said tube, a rod-shapedactuating element for said tool, said actuating element being mountedfor longitudinal displacement in said tube and being articulatedlyconnected to said other handle part via a cylindrical or spherical end,a releasable connection between said tube and actuating element beingreleasably connected to said two handle parts, said tube being pushableinto a tubular receptacle on said one handle part and axially fixabletherein by at least one radially moveable locking body which in an endposition enters into a positive connection with said tube, and aretaining member being mounted on said other handle part, said retainingmember at least partly embracing said cylindrical or spherical end ofsaid actuating element in one end position and being moveable intoanother end position in which said cylindrical or spherical end isremovable from said other handle part in the longitudinal direction,wherein:said locking body is a ball, said radial movement of saidlocking body is delimited by a stop resting against the outer side ofsaid locking body, said stop being formed by a sleeve axiallydisplaceable on said tubular receptacle, said sleeve is displaceablerelative to said locking body such that said locking body is radiallyoutwardly displaceable to different extents, said sleeve forms a stopfor an outer tube which is mounted for axial displacement on said tube,where said sleeve in a forward end position locks the releasablemounting of said tool at the opposite end of said tube, and said sleeveis displaceable in the direction towards said handle parts in order torelease the locking of said tube.
 2. An instrument as defined in claim1, wherein said sleeve is displaced in a spring-loaded manner into saidend position in which the path of displacement of said locking body islimited to the greatest extent.
 3. An instrument as defined in claim 2,wherein said tubular receptacle forms a stop for an outer tube which ismounted for axial displacement on said tube and in the pushed forwardend position locks the releasable mounting of said tool at the oppositeend of said tube.
 4. An instrument as defined in claim 3, wherein saidretaining member is mounted for swivel movement on said other handlepart and in the closed state engages in a section of said actuatingelement adjacent to said spherical or cylindrical end, the outerdimensions of said section transversely to the longitudinal direction ofsaid actuating element being smaller than those of said spherical orcylindrical end.
 5. An instrument as defined in claim 4, wherein saidretaining member has a receiving space for said spherical or cylindricalend with an opening which has a larger region sufficient for passage ofsaid spherical or cylindrical end therethrough and a smaller regionwhich is too narrow for passage therethrough, and in that by movement ofsaid retaining member, said two regions are selectively moveable in thelongitudinal direction of said actuating element in front of itsspherical or cylindrical end.
 6. An instrument as defined in claim 2,wherein said retaining member is mounted for swivel movement on saidother handle part and in the closed state engages in a section of saidactuating element adjacent to said spherical or cylindrical end, theouter dimensions of said section transversely to the longitudinaldirection of said actuating element being smaller than those of saidspherical or cylindrical end.
 7. An instrument as defined in claim 6,wherein said retaining member has a receiving space for said sphericalor cylindrical end with an opening which has a larger region sufficientfor passage of said spherical or cylindrical end therethrough and asmaller region which is too narrow for passage therethrough, and in thatby movement of said retaining member, said two regions are selectivelymoveable in the longitudinal direction of said actuating element infront of its spherical or cylindrical end.
 8. An instrument as definedin claim 1, wherein said tubular receptacle forms a stop for an outertube which is mounted for axial displacement on said tube and in thepushed forward end position locks the releasable mounting of said toolat the opposite end of said tube.
 9. An instrument as defined in claim8, wherein said retaining member is mounted for swivel movement on saidother handle part and in the closed state engages in a section of saidactuating element adjacent to said spherical or cylindrical end, theouter dimensions of said section transversely to the longitudinaldirection of said actuating element being smaller than those of saidspherical or cylindrical end.
 10. An instrument as defined in claim 9,wherein said retaining member has a receiving space for said sphericalor cylindrical end with an opening which has a larger region sufficientfor passage of said spherical or cylindrical end therethrough and asmaller region which is too narrow for passage therethrough, and in thatby movement of said retaining member, said two regions are selectivelymoveable in the longitudinal direction of said actuating element infront of its spherical or cylindrical end.
 11. An instrument as definedin claim 1, wherein said tube is secured against rotation about thelongitudinal axis of said tube by engagement of projections and recesseswhen pushed into said tubular receptacle.
 12. An instrument as definedin claim 11, wherein said projections and recesses are adapted to engagein different angular positions.
 13. An instrument as defined in claim 1,wherein said tubular receptacle is mounted for rotation about itslongitudinal axis on said handle part.
 14. An instrument as defined inclaim 1, wherein said retaining member is constructed as a collet chuckwhich in the released state allows entry or exit of said spherical orcylindrical end by bending open elastically and in the closed stateembraces the latter unreleasably.
 15. An instrument as defined in claim1, wherein said retaining member is mounted for swivel movement on saidother handle part and in the closed state engages in a section of saidactuating element adjacent to said spherical or cylindrical end, theouter dimensions of said section transversely to the longitudinaldirection of said actuating element being smaller than those of saidspherical or cylindrical end.
 16. An instrument as defined in claim 15,wherein said retaining member has a receiving space for said sphericalor cylindrical end with an opening which has a larger region sufficientfor passage of said spherical or cylindrical end therethrough and asmaller region which is too narrow for passage therethrough, and in thatby movement of said retaining member, said two regions are selectivelymoveable in the longitudinal direction of said actuating element infront of its spherical or cylindrical end.
 17. An instrument as definedin claim 16, wherein said retaining member is positionable in its endpositions by elastic detent members.
 18. An instrument as defined inclaim 17, wherein said opening comprises a keyhole-shaped design.